1. Field of the Invention
The present invention relates to a vehicle steering system having a rack bar supporting apparatus, and more particularly, to a vehicle steering system having a rack bar supporting apparatus which prevents the rotation of a rack bar and makes the rack bar supporting apparatus compact by providing a plurality of rack bar supporting apparatuses for elastically supporting the rack bar in the direction of a pinion shaft so that a rack gear formed at the rack bar can be engaged with a pinion gear formed at the pinion shaft.
2. Description of the Related Art
Typically, a vehicle steering system is provided in order to change the traveling direction of a vehicle according to the operation of a driver. The vehicle steering system includes a steering wheel provided at a driver's seat, a steering shaft provided at the lower side thereof, and a gear box being linked with the steering shaft and changing the power transmission direction.
Meanwhile, the gear box includes warm sector type, warm sector roller type, ball-and-nut type, rack-and-pinion type, etc. Among them, the rack-and-pinion type gear box transmits power to a wheel through a pinion gear being rotated from the actuating force generated by a driver and a rack gear contacted with one side of the outer circumference.
FIG. 1 is a cross sectional view showing a conventional rack-and-pinion type gear box. As illustrated therein, the gear box 10 mainly includes a housing 12 provided at the lower end and a rotary valve 11 installed at the upper end so that it can be coupled to the housing 12.
Firstly, inside of the rotary valve 11 is installed an input shaft 13 rotatable with a rotary force generated by a driver. At the lower end of the input shaft 13 is installed a pinion shaft 20 that is connected to the input shaft 13 to be interlocked therewith and has a pinion gear 21 at the outer circumference.
Next, inside the housing 12 is installed a rack bar 30 as a round bar extended in the axial direction, the rack bar 30 having a rack gear 31 which has teeth meshing with the teeth of the pinion gear 21 at one side of the middle of the rack bar 30. At the rear of the rack bar 30, a rack bar supporting apparatus 40 is provided in order to elastically support the rack bar 30 in the direction of the pinion gear 21.
The rack bar supporting apparatus 40 includes a hollow yoke cylinder 50 formed integral with the housing 12 at the rear of the rack gear 31 and a support yoke 60 slidably inserted into the yoke cylinder 50 and having a hemi-circular groove for securely contacting to the rear surface of the rack bar 30.
At the rear of the support yoke 60, a coil type spring 70 is installed so that the support yoke 60 can press the rack bar 30. At the front end of the outer portion of the yoke cylinder 50, a yoke plug 80 is connected and fixed by a screw so that it can support one end of the spring 70.
In addition, at the outer circumference of the yoke plug 80 is installed a lock nut 81 for fixing the yoke plug 80 to the front end of the outer portion of the yoke cylinder 50. Between the support yoke 60 and the rack bar 30, a yoke seat 90 formed of a sheet metal is placed to be tightly contacted with them.
However, in the thusly constructed conventional rack bar supporting apparatus for the vehicle steering system, since the supporting force of the support yoke operates only in one direction of the rear surface of the rack bar, the supporting force is not sufficient, thus making the rack bar rotatable in the circumferential direction.
That is, in a case that there occurs a torsion of the rack bar by the rotation in the circumferential direction because the supporting force operates in only one direction and there is no device for preventing the rotation of the rack bar, an excessive clearance is generated between the pinion gear and the rack gear. This generates noise and abnormal abrasion.